Increase in non-tuberculous mycobacteria isolated from humans in Tuscany, Italy, from 2004 to 2016

Introduction: Non-tuberculous mycobacteria (NTM) include all Mycobacterium species other than Mycobacterium tuberculosis complex and Mycobacterium leprae. NTM are a group of over 150 environmental species; they are generally endowed with low pathogenicity to human, however some species are associated with a variety of human diseases: respiratory tract infection are the most frequent, followed by lymphadenitis in children, disseminated infections in severely immunocompromised patients and skin infections. In Italy, the prevalence of NTM in human infections is largely unknown. The aim of the present survey is to report the epidemiology and recent trend of NTM infections in a region of central Italy, Tuscany, over the last 13 years, and provide a review of the recent literature on NTM isolation rates in different geographic regions. Materials and Methods: The complete collection of NTM strains isolated from 50.150 clinical specimens at the Laboratory of Clinical Mycobacteriology of Pisa University Hospital, Italy, from 1 January 2004 to 31 December 2016 was included. Results: In our setting, in the period 2004-2016 a total of 215 patients had cultures positive for NTM. The number of NTM isolates increased considerably from 5 isolates in 2004 to 36 in 2016; a sharp increase occurred in the last 5 years. Overall, 18 NTM species were isolated; the most common were M. avium, M. intracellulare and M. gordonae detected in respectively in 37.7%, 15.8% and 13.5% of NTM patients. Notably, M. kansasii, a pulmonary pathogen not reported before 2012, was repeatedly isolated in the last 5 years, representing 7,1% of total NTM isolates. In general, NTM isolates were largely prevalent in people older than 60 (59.5%); patients aged 1-10 year-old almost exclusively yielded M. avium and M. intracellulare. Of the 215 NTM clinical isolates, 77.2% were from respiratory specimens, 10.7% from lymph nodes, 2.3% from blood (yielding exclusively M. avium), and the remaining 9.8% from other clinical specimens. Conclusions: The present study provides a snapshot of the prevalent NTM species in our setting and shows an increase in NTM isolation rate, which is in keeping with the general increase in NTM infections reported worldwide in the past two decades, although the distribution of the NTM prevalent species differs by geographic region.